The present invention relates to a neutron flux measuring apparatus or instrument in a reactor pressure vessel in a boiling-water reactor (BWR, ABWR) of a nuclear power plant.
A neutron flux measuring apparatus is used to measure neutron flux, display the power of the reactor because the reactor power is in proportion to the neutron flux and to evaluate the burning degree of a fuel, and also used as a detecting element for protecting the nuclear reactor at a time of excess power output because of quick response to variation of the power.
This neutron flux measuring apparatus consists of a neutron flux detector and a measuring device amplifying and displaying the signal from the detector. Since the measuring range is quite wide, it is necessary to accurately measure the power output from rated power to about 10xe2x88x9210 times as high as the rated power and it is, therefore, difficult to measure entire range using one type of a measuring apparatus. For that reason, start-up range neutron monitor (to be referred to as xe2x80x98SRNMxe2x80x99 hereinafter) detectors for measuring low power ranges and local power range monitor (to be referred to as xe2x80x98LPRMxe2x80x99 hereinafter) detectors for measuring high power ranges are used. A set of four LPRM detectors are vertically arranged in the reactor pressure vessel in axial direction and form a local power range monitor detector assembly as a whole.
Conventionally, eight or ten SRNM detectors are normally installed, whereas 52 LPRM detector assemblies (or 208 detectors) are installed in an ABWR. The SRNM detectors and LPRM detector assemblies are arranged separately in the reactor pressure vessel.
Now, description will be given to a case where ten SRNM detectors and 52 LPRM detector assemblies (208 detectors) are installed.
FIG. 12 shows the arrangement of SRNM detectors and LPRM detector assemblies at a reactor core in a conventional advanced boiling-water reactor (to be referred to as xe2x80x98ABWRxe2x80x99 hereinafter).
As shown in FIG. 12, ten SRNM detectors (A, B, C, D, E, F, G, H, J, L) are equally arranged at a reactor core 1. Since one operation (arithmetic) unit is arranged for each SRNM detector, an SRNM consists of ten SRNM detectors and ten operation units.
The detectors are used as detecting elements for the protection of the reactor when the power output thereof is in excess and the detectors detect an abnormal transient change which takes place during operation, emit a reactor emergency shutdown (reactor scram) signal and shut down the reactor. To detect such an abnormal transient change, the detectors is divided into reactor protection system divisions (sections), respectively. The reactor protection system divisions are composed of double special logic structural circuits such as xe2x80x9c1 out of 2xe2x80x9d and xe2x80x9c2 out of 4xe2x80x9d and prevents unnecessary reactor shutdown due to erroneous operation and abnormal operation due to inactive operation.
The SRNM operation unit calculates a neutron flux level in the detector, calculates the increase degree of a neutron flux in the form of period (reactor period) and emits a control rod pull-out prohibiting signal or a scram signal when the calculated period is below a predetermined period, thus functioning as a safety protection system.
FIG. 13 shows that the SRNM detectors are divided into the reactor protection system divisions.
As shown in FIG. 13, the SRNM detectors (A, E, J) are in a division (section) I and the SRNM detectors (B, F) are in a division II. The SRNM detectors (C, G, L) are in a division III and the SRNM detectors (D, H) are in a division IV. The SRNM detectors are divided into the divisions I to IV each including tow or three ones.
Meanwhile, the LPRM consists of 52 detector assemblies (208 detectors) and 16 operation units, and the 52 detectors and the four operation units are partitioned into each of the four sections, as shown in FIG. 12.
The LPRM operation units or average power range monitor (to be referred to as xe2x80x98APRMxe2x80x99 hereinafter) operation units are allotted with signals of the respective LPRM detectors in accordance with the reactor protection system divisions, standardize and calibrates the signals to local power level using signals from a TIP traversing incore probe (to be referred to as xe2x80x98TIPxe2x80x99 hereinafter) detector or a gamma thermometer. The signals are further fed to the APRON operation units in which signals from LPRM detectors belonging to the respective APRM channels are averaged thereby to create APRM signals. Each of the APRM operation units generates a trip signal such as a control rod pull-out prohibition and scram if the APRM signal exceeds a predetermined APRM signal level and activates scram by means of the double special logic structural circuits such as xe2x80x9c1 out of 2xe2x80x9d and xe2x80x9c2 out of 4xe2x80x9d described above.
In the meantime, it is required for the detectors such as the SRNM detectors as well as their respective operation units to be regularly inspected and maintained. While maintaining and adjusting these detectors and operation units, if it is detected that the data during adjustment is abnormal, a reactor scram signal is outputted and the reactor is shut down. For this reason, at the time of the maintenance and adjustment of the detectors or operation units themselves, the detectors or units are precluded from normal monitoring, which is referred to as bypassing. To execute bypassing, the detectors are divided into groups other than the reactor protection system divisions in the SRNM monitor.
This is because the range the SRNM detectors can monitor corresponds to the radius of the reactor core. The detector arrangement in the reactor as well as the bypass groups are set such that even if part of SRNM detectors or operation units are bypassed, two or more detectors in different reactor protection system divisions are present within a distance corresponding to the radius of the reactor from the arbitrary position of a control rod in consideration of monitoring an arbitrary range in the reactor without adversely influencing the reactor emergency shutdown function. With the ten detecors being provided, it is impossible to make the bypass groups coincident with the reactor protection system divisions.
Now, it is assumed that the bypass groups are made coincident with the reactor protection system divisions in the conventional start-up range monitor arrangement. In FIG. 13, if the SRNM detectors (A, F, L, D) are bypassed, there is no detector which can monitor the upper right range on the reactor core plane shown in FIG. 12 and the above conditions cannot be satisfied.
It is, therefore, necessary to set bypass groups different from the reactor protection system divisions.
FIG. 14 shows the bypass groups for the SRNM detectors.
As shown in FIG. 14A, the SRNM detectors (A, B, F, G) are sectioned in a bypass group {circle around (1)} and the SRNM detectors (C, E, H) are sectioned in a bypass group {circle around (2)}. The remaining SRNM detectors (D, J, L) are sectioned in a bypass group {circle around (3)}.
Further, as shown in FIG. 14B, since only one detector in the respective bypass groups from {circle around (1)} to {circle around (3)} is bypassed, the allowable number of bypassed detectors is up to three.
It is noted that since an operation unit is provided per detector in the SRNM monitor, detector bypassing and operation unit bypassing are carried out by the same operation.
Meanwhile, many LPRM detectors ace arranged and necessary number of detectors for monitoring average power output are arranged in the reactor for each reactor protection system division. For this reason, it is possible to make the bypass groups coincident with the reactor protection system divisions and to bypass a plurality of detectors to the extent that the number of detectors is not below the number required for APRM operation. Furthermore, even if all of the detectors belonging to an optional division (section) are bypassed, no problem occurs to the reactor emergency shutdown function as long as the remaining sections are in a state in which the average power output of the reactor core can be monitored. Thus, the operation unit can be commonly used for a plurality of detectors, and the bypassing of operation units is made allowable.
Recently, a reactor pressure vessel is becoming larger in size so to increase reactor power, and accordingly, it has been required to increase the number of SRNM detectors which number has been conventionally eight to ten.
If the number of the SRNM detectors increases, however, many guide tubes and flanges must be provided in the reactor when the SRNM detectors are installed, which involves cost increasing. In addition, as the number of detectors increases, design, operation and the like become increasingly complicated, such as the interference of the position, at which instrumentation is arranged, with the support structure below the reactor core, thus providing a problem.
Furthermore, it is not allowed to bypass SRNM detectors in an optional one division among the reactor protection system divisions altogether (which bypassing will be referred to as section xe2x80x98bypassing"" hereinafter) at the time of starting the reactor from the viewpoint of monitoring reactor power output at an arbitrary position in the reactor core. Therefore, if a plurality of detectors shares an operation unit for each section (division), the operation unit cannot be bypassed to thereby cause a problem in the operation. For this reason, an operation unit is required per detector in the start-up range monitor, and as the number of detectors increases, the number of operation units needs to increase.
Specifically, in a present advanced boiling-water reactor (ABWR) plant, a neutron flux measuring apparatus is provided with ten SRNM detectors and 52 LPRM detectors, which detectors are provided individually in the reactor pressure vessel. For this reason, the total number of the neutron detectors is 62 and the installation of guide tubes and flanges in the reactor for the 62 detectors is required. Besides, the 26 operation units for monitoring start-up ranges and local power ranges. As the number of detectors increases, cost disadvantageously increases, which is an economic problem.
Moreover, the reactor protection system divisions sections shown in FIG. 13 and the bypass groups shown in FIG. 14 differ in the allocation of detectors. This makes the recognition and dealing of detectors laborious for operators involved with the reactor operation, thereby causing a problem in the operation.
The present invention has been made to solve the defects or problems encountered in the prior art mentioned above and the first object of the present invention is to provide a neutron flux measuring apparatus having increased cost-efficiency without deteriorating monitoring performance by jointly using detectors and operation units to thereby reduce the number of necessary detectors and operation units.
It is another object of the present invention to provide a neutron flux measuring apparatus capable of reducing labor during operation of a reactor and enhancing operability by making reactor protection system divisions and bypass groups have the same constitution in the start-up range neutron monitor.
These and other objects can be achieved according to the present invention by providing, in one aspect, a neutron flux measuring apparatus, adapted to a boiling-water reactor (BWR) of a nuclear power plant and an advanced boiling-water reactor (ABWR) of a nuclear power plant, for measuring a neutron flux in a reactor pressure vessel, said neutron flux measuring apparatus comprising:
a neutron flux detector assembly incorporating a local power range monitor detector assembly and a start-up range neutron monitor detector;
a preamplifier amplifying a detector signal obtained from said start-up range neutron monitor detector;
a start-up range neutron monitor operation unit operating, indicating and monitoring the amplified signal of the start-up range neutron monitor detector; and
a local power range monitor operation unit operating, indicating and monitoring a signal obtained from said local power range monitor detector.
In preferred embodiments in this aspect, the start-up range neutron monitor operation unit and the local power range monitor operation unit are integrated into a signal unit.
The neutron flux measuring apparatus may further comprises reactor mode monitoring means for inputting and monitoring a state of a reactor mode switch and calculation frequency switching means for making high a calculation frequency of a start-up range monitor operation function and making low a calculation frequency of a power range monitor operation function within an integrated operation unit of the neutron flux measuring apparatus while a reactor mode is in a start-up state and for conversely making low a calculation frequency of the start-up range monitor operation function and making high a calculation frequency of the power range monitor operation function while the reactor mode is in an operation state.
The start-up range neutron monitor detector includes a bypass group having same detector channel arrangement as a detector channel arrangement of a reactor protection system division.
The neutron flux detector assembly includes the start-up range neutron monitor detector coated with an insulation layer having resistance to an environment within a reactor pressure vessel.
The neutron flux detector assembly includes the start-up range neutron monitor detector installed in a small-diameter hollow tube.
Each of the reactor protection separation divisions is provided with a plural signal processing start-up range neutron monitor operation unit, which operates, indicates and monitors signals of a plurality of start-up range neutron monitor detectors belonging to the same reactor protection system division. Bypass means may be further provided for bypassing a plural signal processing start-up range neutron monitor operation function belonging to one of the reactor protection system divisions.
A plurality of neutron flux detector assemblies, each incorporating a start-up range neutron monitor detector, are arranged in vicinity of a center of a reactor core, the number of the neutron flux detector assemblies being the same as the number of reactor protection system divisions, the neutron flux detector assemblies, the number of which is twice or more of the number of reactor protection system divisions, are arranged on a peripheral portion surrounding the neutron flux detector assemblies arranged in vicinity of a center of the reactor core, and there is further provided start-up range neutron monitor detector bypass groups, the number of which is the same as the number of the reactor protection system divisions, including a set of a start-up range neutron monitor detector incorporated into one neutron flux detector assembly in vicinity of a center and the start-up range neutron monitor detector incorporated into two or more neutron, flux detector assemblies on the peripheral portion, the start-up range neutron monitor detectors being allotted to the reactor protection system divisions with the same groups as the bypass groups. There may be further provided bypass means for bypassing an operating, indicating and monitoring function for an optional one of signals from the start-up range neutron monitor detectors belonging to the same reactor protection system division.
The above mentioned objects scan be achieved according to the present invention by providing, in a second aspect, a neutron flux measuring apparatus, adapted to a boiling-water reactor (BWR) of a nuclear power plant and an advanced boiling-water reactor (ABWR) of a nuclear power plant, for measuring a neutron flux in a reactor pressure vessel, the neutron flux measuring apparatus comprising:
a plurality of neutron flux detector assemblies each incorporating a start-up range monitor detector, each of the plurality of neutron flux detector assemblies comprising a local power range monitor detector, a start-up range neutron monitor detector, calibrating means for calibrating sensitivity of the local power range monitor detector and a cover tube incorporating the local power range monitor detector, the start-up range neutron monitor detector and the calibrating means;
a plurality of neutron flux detector assemblies each comprising the local power range monitor detector, the calibrating means and said cover tube;
a preamplifier amplifying a detector signal obtained from the start-up range neutron monitor detector;
a start-up range neutron monitor operation unit operating, indicating and monitoring the amplified signal obtained from the start-up range neutron monitor detector;
a local power range monitor operation unit operating, indicating and monitoring a signal obtained from the local power range monitor detector; and
an average power range monitor operation unit averaging, indicating and monitoring signals obtained from a plurality of local power range monitor detectors.
In preferred embodiment of this second aspect, the start-up range neutron monitor operation unit and the local power range monitor operation unit are integrated into a signal unit. There may be further provided reactor mode monitoring means for inputting and monitoring a state of a reactor mode switch and calculation frequency switching means for making high a calculation frequency of a start-up range monitor operation function and making low a calculation frequency of a power range monitor operation function within an integrated operation unit of the neutron flux measuring apparatus while a reactor mode is in a start-up state, and for conversely making low a calculation frequency of the start-up range monitor operation function and making high a calculation frequency of the power range monitor operation function while the reactor mode is in a run mode state.
The average power range monitor operation unit, the start-up range neutron monitor operation unit and the local power range monitor operation unit are integrated into a single unit. The start-up range neutron monitor detector includes a bypass group having same detector channel arrangement as a detector channel arrangement of a reactor protection system division.
Each of the neutron flux detector assemblies includes a start-up range neutron monitor detector coated with an insulation layer having resistance to an environment within a reactor pressure vessel.
The neutron flux detector assembly includes a start-up range neutron monitor detector installed in a small-diameter hollow tube.
Each of the reactor protection system divisions is provided with a plural signal processing start-up range neutron monitor operation unit, which operates, indicates and monitors signals of a plurality of start-up range neutron monitor detectors belonging to the same reactor protection system division. The plural signal processing start-up range neutron monitor operation unit, at least one type of local power range, monitor operation unit or average power range monitor operation unit are commonly integrated into a single unit per reactor protection system division.
There is further provided with bypass means for bypassing a plural signal processing start-up range neutron monitor operation function belonging to one of the reactor protection system divisions. There may be further provided with bypass means for bypassing an average power range monitor operation function belonging to one of reactor protection system divisions. There may be further provided with bypass means for bypassing an integrated monitor operation unit belonging to one of reactor protection system divisions and for simultaneously bypassing an average power range monitor operation function and a plural signal processing start-up range neutron monitor operation function.
There may be further provided with a automatic correction means for correcting a start-up range neutron monitor output obtained as a result of operating a start-up range neutron monitor signal using an average power range monitor output which is a result of averaging operation of said average power range monitor operation unit, and may further provided with a reactor run mode monitoring means for inputting and monitoring a state of a reactor mode switch and automatic correction means for correcting a start-up range neutron monitor output and for making the start-up range neutron monitor output coincident with an average power range monitor output when a reactor mode is switched from start-up to operation or operation to start-up.
Alarm determining means may be further provided for determining whether an average power range monitor output reaches a downscale alarm value and automatic correction means for correcting the start-up range neutron monitor output using a signal of the alarm determining means and for making the start-up range neutron monitor output coincident with the average power range monitor output. In an alternation, alarm determining means may be provided for determining whether an average power range monitor output reaches an upscale alarm value in a mode other than reactor operation mode and automatic correction means for correcting the start-up range neutron monitor output using a signal of the alarm determining means and for making the start-up range neutron monitor output coincident with the average power range monitor output.
There may be further provided with automatic correction means for inputting a signal of a local power range monitor detector arranged closest to the start-up range neutron monitor detector into the average power range monitor operation unit into which a signal of the start-up range neutron monitor detector is inputted and for correcting the start-up range neutron monitor output using a local power range monitor output obtained from an operation result of operating the local power range monitor detector signal. In an alternation, there may be provided automatic correction means for taking in a reactor operating parameter and calculating an output distribution in the reactor using a three-dimensional BWR simulation function incorporated into a reactor core performance monitoring unit connected to calibrating means, for obtaining and transmitting a value read by a start-up range neutron monitor detector from the power output distribution calculation result, for correcting a start-up range neutron monitor output and for making the start-up range neutron monitor output coincident with the read calculation value.
Furthermore, a plurality of neutron flux detector assemblies, each incorporating a start-up range neutron monitor detector, are arranged in the vicinity of a center of a reactor core, the number of the neutron flux detector assemblies being the same as the number of reactor protection system divisions, the neutron flux detector assemblies, the number of which is twice or more of the number of reactor protection system divisions, are arranged on a peripheral portion surrounding the neutron flux detector assemblies arranged in the vicinity of a center of the reactor core, and further comprising start-up range neutron monitor detector bypass groups, the number of which is the same as the number of the reactor protection system divisions, including a set of a start-up range neutron monitor detector incorporated into one neutron flux detector assembly in the vicinity of a center and the start-up range neutron monitor detector incorporated into two or more neutron flux detector assemblies on the peripheral portion, the start-up range neutron monitor detectors being allotted to the reactor protection system divisions with the same groups as the bypass groups.
There may be further provided with bypass means for bypassing an operating, indicating and monitoring function for an optional one of signals from start-up range neutron monitor detectors belonging to the same reactor protection system division.
According to the above first aspect of the present invention, it is made unnecessary to install a start-up range neutron monitor detector solely in a reactor pressure vessel by integrating the start-up range neutron monitor detector and the local power range monitor detector assembly into a single detector assembly and installing these detectors into the reactor pressure vessel. Accordingly, it becomes possible to reduce the number of neutron detector assemblies, neutron detector installation flanges and neutron detector guide tubes installed in the reactor pressure vessel.
According to the second aspect of the present invention, it is made unnecessary to install a start-up range neutron monitor detector solely in a reactor pressure vessel by incorporating the local power range monitor detector, start-up range neutron monitor detector and calibrating means into a single cover tube and installing them into the reactor pressure vessel. Accordingly, it becomes possible to reduce the number of neutron detector assemblies, neutron detector installation flanges and neutron detector guide tubes arranged in the reactor pressure vessel.
Furthermore, according to the preferred embodiments of the above first and second aspect, the following advantageous functions and effects will be achieved.
The number of operation units can be reduced by integrating the local power range monitor operation unit and the start-up range neutron monitor operation unit.
It becomes possible to continuously monitor the reactor power level from the reactor start-up to power output operation using one operation unit, thereby enhancing monitoring performance. The number of the start-up range neutron monitor detectors arranged in the reactor pressure vessel is increased to make allowable number of bypassed detectors four, and four bypass groups are provided. Since the neutron flux detector assembly incorporating a start-up range neutron monitor detector is applied and installed in the reactor pressure vessel, the number of neutron detector assemblies arranged in the reactor does not increase. Moreover, by making the bypass groups for the start-up range neutron monitor identical to the reactor protection system divisions, operators can avoid feeling confused during the bypass operation and labor can be thereby reduced.
Furthermore, by coating the start-up, range neutron monitor detector with an insulating layer resistant to the environment within the reactor pressure vessel, the start-up range neutron monitor detector can be installed in the reactor so as not to contact the detector with reactor water as in the case of a conventional state in which the start-up range neutron monitor detector is installed in the reactor, and noise can be prevented from entering the start-up range monitor. Still furthermore, by applying, in particular, alumina to this insulating layer, it is possible to isolate the start-up range neutron monitor detector from reactor water.
Still furthermore, by installing the start-up range neutron monitor detector in the hollow tube of a small diameter, the start-up range neutron monitor detector can be installed in the reactor so as not to contact the detector with reactor water as in the case of the conventional state in which the start-up range neutron monitor detector is installed in the reactor, and noise can be prevented from entering the start-up range monitor. Moreover, by using, in particular, stainless steel for this hollow tube, it becomes possible to isolate only the start-up range neutron monitor detector from reactor water.
Still furthermore, by performing a plurality of arithmetic operations altogether for every section, it is possible to reduce the number of detectors without increasing the number of operation units and to operate the detectors and operation units for every reactor protection system division, thereby facilitating the operation and maintenance.
Still furthermore, it becomes possible to reduce the number of operation units and to continuously monitor the reactor power level from the reactor start-up to power output operation using a single operation unit. Thus, not only monitoring performance enhances but also the number of detectors can be increased without increasing the number of operation units due to the fact that a plurality of arithmetic operations are performed altogether for every section. In addition, it is possible to operate the detectors and operation units for every division (section), thereby facilitating the operation and maintenance.
Still furthermore, by increasing the number of start-up range neutron monitor detectors installed in the reactor pressure vessel, it is possible to bypass, maintain and test all the start-up monitoring functions in one division without adversely influencing the function of the start-up range monitors as the reactor protection system division.
Still furthermore, it becomes possible to bypass, maintain and test all the average power range monitoring function in one section without adversely influencing the function of the average power range monitors as the reactor protection system.
Still furthermore, it becomes possible to carry out the maintenance and testing without adversely influencing the function of the neutron flux measuring apparatus as the reactor protection system divisions by bypassing the operation unit in the divisions.
Still furthermore, by providing the automatic correction means, adjustment operation by operators or maintenance personnel for correcting the start-up range monitor output as required in the conventional case is made unnecessary, thereby greatly enhancing operability and maintenability.
Still furthermore, it becomes possible to monitor reactor power outputs as continuous values before or after an operator switches the reactor mode, thereby enhancing monitoring performance.
Still furthermore by correcting the irregularity of directions for the start-up range neutron monitor output before the reactor mode switching operation using the alarm determining means at a time when the power output of the reactor is rising, the output range, in which the reactor mode can be switched, is widened and operability is enhanced.
Still furthermore, by correcting the irregularity of the start-up range monitoring direction when the reactor output power decreases before the switching operation of the reactor run mode, the power output range, in which the reactor mode can be switched, is widened and operability is enhanced.
Still furthermore, the reliability in the monitoring of local power output using the start-up range monitor output enhances. The start-up range monitor outputs including sensitivity change due to the irradiation of a fission detector in the reactor can be corrected.
Still furthermore, by installing the detectors in different reactor divisions in the vicinity of the center, detectors in different divisions are arranged in the vicinity of the center during the section (division) bypassing. Accordingly, it becomes possible to monitor the overall reactor without adversely influencing reactor emergency shutdown function. In addition, by two or more detectors per detector bypass group are arranged on the peripheral portion so as to compensate for the monitoring range of the detectors in the vicinity of the center while all of the detectors in the vicinity of the center are bypassed, it becomes possible to monitor the overall reactor and the operability can be hence enhanced.
Still furthermore, up to one start-up range neutron monitor detector per reactor protection system division is permitted to be bypassed, whereby the operators and maintenance personnel can easily manage, monitor and operate the detector bypassing for every protection system division for the start-up range neutron monitor.
Finally, in the xe2x80x98start-up xe2x80x99 mode, the scram function executed by the start-up range neutron monitor is the most important among the reactor protection system functions In the run (operation) mode, the scram function executed by the average power range monitor is the most important among the reactor protection system functions. Thus, their response is significant. According to the present invention, which is provided with calculation frequency switching means, it is possible to obtain a neutron flux measuring apparatus without adversely influencing the above-mentioned functions even if the operation unit in the neutron flux measuring apparatus is shared by the start-up range neutron monitor and the power range monitor.
The nature and further characteristic features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings.